The present invention pertains to a method for controlling the hydraulic pressure in a power steering device that serves to supply compressed oil to the left and the right chamber of a power steering cylinder via a rotary slide valve with the aid of a pump, wherein a reaction piston arranged on the input shaft in axially movable and rotationally rigid fashion, connected to the control sleeve of the rotary slide valve via an elastic rotary coupling is inserted between the input shaft and the control sleeve of the rotary slide valve, and wherein a hydraulic reaction device controlled by a control unit with dependence on speed and which serves to control the reaction pressure is arranged in a return line for the hydraulic medium which leads away from the reaction piston. The invention additionally pertains to a power steering device for implementing said method.
Power steering devices of this type are generally known, e.g., from DE 42 42 441 C1. A hydraulic reaction device that is controlled with dependence on speed is arranged in a return line for the hydraulic medium that is arranged on the housing within the region of the reaction piston and leads either directly or indirectly to the reservoir for the hydraulic medium. In this case, the reaction device is a conventional solenoid valve controlled by a control unit with dependence on speed. When driving at slow speeds, e.g., during parking, the return pressure is increased with the aid of this speed-controlled solenoid valve such that the manual steering moment is reduced due to the retroeffect on the reaction piston.
One disadvantage of known methods or systems of this type can be seen in the fact that the increased return pressure also acts upon the seals of the steering rack, i.e., an undesirable increase in the steering rack restoring force results. In order to attain an essentially identical steering rack power level, it is necessary to adapt the undercarriage correspondingly.
One additional disadvantage of the increased return pressure can be seen in the inevitable increase in the oil temperature. In addition, an increased pressure is associated with severe noise problems.
Originating from this state of the art, the present invention is based on the objective of modifying a method for controlling the hydraulic pressure in a power steering device of the initially mentioned type in such a way that the most uniform steering rack power level possible is attained and an unnecessary increase in the oil temperature is simultaneously prevented. The invention additionally proposes a corresponding power steering device.
With respect to the method according to the invention, said objective is attained by determining the changes in the hydraulic pressure and utilizing these changes as control parameters for the hydraulic reaction device that is controlled with dependence on speed in addition to the parameter speed.
The invention proposes a simple control method in which the parameter change in hydraulic pressure is monitored in addition to the parameter speed. The changes in the system pressure are advantageously monitored.
In this case, one utilizes the increase in the system pressure once the rotary slide valve is activated. In the restoring state of the steering system, the rotary slide valve is moved into its neutral position and the system pressure drops to the respective reaction pressure defined by the control unit.
However, the reaction pressure that is controlled with dependence on speed is, in principle, only required for altering the activation moment of the rotary slide valve with dependence on speed. In this respect, the hydraulic reaction device that is controlled with dependence on speed, e.g., a solenoid valve, can be controlled such that the reaction pressure is only built up if the rotary slide valve is activated.
Consequently, the invention proposes to render the hydraulic reaction device controlled with dependence on speed ineffective if the determined system pressure drops or is identical to the reaction pressure. The system pressure is determined over a preset duration. If the dropping values are determined, the hydraulic reaction device controlled with dependence on speed is rendered ineffective. For this purpose, the invention proposes to bypass this device or, in the case of an electrohydraulic device, render the device without current.
However, if an increasing system pressure is determined, the hydraulic reaction device controlled with dependence on speed is activated.
In order to determine the system pressure, one embodiment of the invention proposes to utilize a pressure sensor. This pressure sensor is advantageously utilized for determining the system pressure in a corresponding line and connected to the control unit.
An alternative proposal of the invention pertains to the advantageous utilization of a proportional pressure regulator that, according to one embodiment of the invention, is arranged between a line that conveys the system pressure and a line that conveys the reaction pressure. In this case, the proportional pressure regulator is advantageously controlled by the system pressure.
The method according to the invention allows the simple activation of the hydraulic reaction device controlled with dependence on speed with dependence on the system pressure, i.e., an increased reaction pressure is only generated if the activation moment of the rotary slide valve actually needs to be changed.
With respect to the device, the aforementioned objective is attained with a power steering device that serves for supplying compressed oil to the left and the right chamber of a power steering cylinder via a rotary slide valve with the aid of a pump, wherein a reaction piston arranged on the input shaft in axially movable and rotationally rigid fashion and connected to the control sleeve of the rotary slide valve via an elastic rotary coupling is inserted between the input shaft and the control sleeve of the rotary slide valve, and wherein a hydraulic reaction device controlled by a control unit with dependence on speed and which serves to control the reaction pressure is arranged in a return line for the hydraulic medium which leads away from the reaction piston. This power steering device is characterized by a device for determining changes in the hydraulic pressure which are used for controlling the hydraulic reaction device controlled with dependence on speed.
The power steering device according to the invention is very suitable for use in connection with the aforementioned method. This power steering device is advantageously utilized for determining changes in the system pressure.
According to one embodiment of the invention, the power steering device consists of a proportional pressure regulator that is advantageously arranged between a line that conveys the system pressure and a line that conveys the reaction pressure and connected to an unpressurized return line. If this proportional pressure regulator is controlled by the system pressure, the proportional pressure regulator is opened when the rotary slide valve is in a neutral position, namely because the system pressure corresponds to the reaction pressure. Consequently, the hydraulic oil flows back to the reservoir in unpressurized fashion. However, if the rotary slide valve is activated, the system pressure is increased and the direct return of the oil to the reservoir is blocked via the proportional pressure regulator. Consequently, the oil is forced to flow via the solenoid valve that is controlled with dependence on speed, i.e., the power steering system is activated due to the increase in the reaction pressure.
An alternative embodiment of the invention proposes that the device for determining changes in the hydraulic pressure consist of a pressure sensor. This pressure sensor is advantageously arranged in a line that conveys the system pressure, and connected to the control unit. This control unit regulates the hydraulic reaction device that is controlled with dependence on speed, e.g., a solenoid valve, with dependence on speed as well as the changes in the system pressure.
The invention discloses a new power steering valve that is realized by simple modifications to generally known power steering valves and in which changes in the reaction pressure are only produced if required.